1. Field of the Invention
This invention relates to fuel ignition systems, and more particularly to a self-checking, dual channel fuel ignition system providing automatic shut off of fuel in the event of loss of flame or ignition sparks.
2. Description of the Prior Art
Fuel ignition systems generally include an igniter circuit having a pulse generator operable when enabled to generate high voltage pulses which are applied to a pair of ignition electrodes positioned adjacent to a fuel outlet. The electrodes are spaced apart to provide a gap therebetween such that the high voltage pulses applied to the electrodes produce ignition sparks for igniting fuel emanating from the outlet to establish a flame. When a flame is established, a flame sensing circuit disables the pulse generator. In the event of a flame out, the flame sensing circuit reenables the pulse generator to attempt reignition of the fuel.
In certain igniter circuits, a pulsating control device is employed for disabling the pulse generator whenever a flame is established. In ignition systems energized from an AC voltage source, the cyclical AC voltage can be used to drive such control device. However, in ignition systems energized from a DC source, such as may be used in a heating system for a mobile recreational vehicle, an inverter circuit is needed to provide the required pulsating drive resulting in additional cost to the system.
A further consideration is that in the event of a flame out condition, reignition of the fuel depends on the operability of the spark generator of the igniter circuit. Thus, in the event of a malfunction of the spark generator, unburned gas will be wasted as the igniter circuit cycles to attempt reignition. Moreover, since the igniter circuit usually is located in an enclosure and is generally not readily accessible to view, failure of the spark generator may go unnoticed for a long time.
In my U.S. Pat. No. 3,914,092, which was issued on Oct. 21, 1975, there is disclosed a direct spark ignition system employing a sampling spark sensor. The system includes an ignition circuit for generating sparks for igniting fuel discharged by a fuel outlet, an energizing circuit controlled by the ignition circuit to operate fuel valves to supply fuel to the fuel outlet, and a flame sensing circuit operable when a flame is established to normally disable the ignition circuit and to periodically enable the ignition circuit to test the operability of the ignition circuit and to test for the presence of a flame.
The system automatically tests the operability of the ignition circuit and provides automatic shut off of the fuel supply in the event of loss of flame or loss of ignition sparks. The system also provides remote indication of loss of spark or flame.